With the support of this grant we propose to study carbonic anhydrase activity in different isolated and separated cell fractions and to attempt a correlation between parietal cell mass and this enzyme activity. With monolayers formed by separated cell fractions, movement of ions and potential differences across the layer will be studied. Using a weak baseline, methylamine, attempts will be made to measure H+ion formation by the parietal cell. Gastric assays and gastric cell population in isolated cell fractions from the plyoric antrum will be made. Chief cell fractions will be used for determining pepsinogen activity and correlated with chief cell counts. Further attempts will be made to determine the ionic content of individual isolated cells by electron probe microanalysis.